AP Thermal Unit Review

A thermodynamic system is taken from an initial state X along the path XYZX as shown in the PV-diagram. For the process Y-→Z, Q is greater than zero and W<0 & U = 0

• W < 0 & U =0

• W=0 & U<0

• W=0 & U>0

• W>0 & U=0

• W > 0 & U > 0

An ideal gas in a closed container initially has volume V, pressure P. and Kelvin temperature T. If the temperature is changed to 3T, which of the following pairs of pressure and volume values is possible?

• 3P and V

• P and V/3

• P/3 and V

• 3P and 3V

• P and V

Gas in a chamber passes through the cycle ABCA as shown in the diagram above. In the process AB, 12 joules of heat is added to the gas. In the process BC, no heat is exchanged with the gas. For the complete cycle ABCA, the work done by the gas is 8 joules. How much heat is added to or removed from the gas during process CA?

• 20 J is removed

• 4 J is removed

• 4 J is added

• 20 J is added

• No heat is added to or removed from the gas

In each cycle of a certain Carnot engine, 100 joules of heat is absorbed from the high-temperature reservoir and 60 joules is exhausted to the low-temperature reservoir. What is the efficiency of the engine?

• 40%

• 60%

• 67%

• 150%

• 167%

An ideal gas is initially in a state that corresponds to point 1 on the graph above, where it has pressure p1, volume V1, and temperature T1. The gas undergoes an isothermal process represented by the curve shown, which takes it to a final state 3 at temperature T3. If T2 and T4 are the temperatures the gas would have at points 2 and 4, respectively, which of the following relationships is true?

• T1 < T3

• T1 < T2

• T1 < T4

• T1 = T2

• T1 = T4

Which of the following statements is NOT a correct assumption of the classical model of an ideal gas?

• The molecules are in random motion.

• The volume of the molecules is negligible compared with the volume occupied by the gas.

• The molecules obey Newton's laws of motion.

• The collisions between molecules are inelastic.

• The only appreciable forces on the molecules are those that occur during collisions.

A gas with a fixed number of molecules does 32 J of work on its surroundings, and 16 J of heat are transferred from the gas to the surroundings. What happens to the internal energy of the gas?

• It decreases by 48 J.

• It remains the same.

• It increases by 16 J.

• It increases by 48 J.

• It decreases by 16

A gas can be taken from state a to c by two different reversible processes, ac or a→b→c. During the direct process a→c, 20.0 J of work are done by the system and 30.0 J of heat are added to the system. During the process a→b→c, 25.0 J of heat are added to the system. How much work is done by the system during a→b→c?

• 5.0 J

• 10.0 J

• 15.0 J

• 20.0 J

• 25.0 J

The average speed of the atoms of a gas at 100 K is 200 m/s. What would most nearly be the average speed of the atoms at 300 K?

• 67 m/s

• 140 m/s

• 200 m/s

• 350 m/s

• 600 m/s

A 200 gram sample of copper is submerged in 100 grams of water until both the copper and water are at the same temperature. Which of the following statements would be true?

• The molecules of the water and copper would have equal average speeds

• The molecules of the water and copper would have equal average momenta

• The molecules of the water and copper would have equal average kinetic energies

• The water molecules would have twice the average momentum of the copper molecules

• The copper molecules would have twice the average speed of the water molecules